Form of coprophilia practiced by lesbians in the United Kingdom. One partner defecates into the other's vagina, which is held open, often with the aid of a speculum. They then proceed to suck their feces back out of their partner's vagina and ingest it.

Vanessa was eagerly clarking some nice steamy nuggets right out of Sarah's minge.

When an upper-classman dates a younger female at a school. "Clarkers" will usually have a string of failed relationships that only lasted for a few weeks. Those who clark usually do so because they are infamous around school and no girls in their grade want to date them, it is because of this the clarker usually takes advantage of the newer girl's ignorance pertaining to who the clarker really is.

The bigger the age difference between the clarker and the victim, the more pathetic it becomes (ie a junior dating a freshman is worse than a sophmore dating a freshman)
Someone is not clarking if they have been dating the younger girl for more than 6 months, or if they have only clarked once.

Person 1: "Dude Josh was picking his nose in class again."
Person 2: "The guy who shit himself in math last year?"
Person 1: "Yeah! I heard he has another freshman girlfriend this year."
Person 2: "Probably because she doesn't know how gross he is."
Person 1: "Poor girl doesn't even realize she's a victim of clarking."
Person 2: "Wait wasn't he with Taleene last week?"

having sex with a woman and her daughters (named after former British member of parliament Alan Clark who revealed that he had slept with Valerie Harkess, the wife of a South African judge, and both of their daughters)

When one gets high and engages into a sort of pseudo-profound speech that he or she believes is highly interesting and sensible while his or her audience half-listens, becomes confused, and informs the speaker that he or she has just “clarked” and has not made any sense whatsoever, at which point, the speaker also realizes he or she is making no sense.

(After non-sensibly rambling for 5 minutes), “Dude, you just clarked. You’ve been clarking for five minutes."